High density connector system

ABSTRACT

An electrical connector illustrated as a plug and receptacle is disclosed. In one embodiment, the connector includes a base member having a plurality of bores. A first plurality of contact elements is positioned in certain of the bores. The tail portion of each contact element extends a distance beyond the base member. A second plurality of contact elements is positioned in others of the bores. Insertion of the tail portion of the second plurality of contact elements into a circuit board is sufficient to hold the tail portions of the first plurality of contact elements against the circuit board. It is preferred for the tail portions of the second plurality of contacts to be capable of axial movement when a compression force is applied. In another embodiment, the connector includes a frame and a layer of contact elements, wherein each of the contact elements includes a forward end and a tail portion. The ends of the tail portions are positioned proximate the bottom surface of the frame. A plurality of shaped fusible elements, for example, solder balls, are located proximate the ends of the tail portions. In such an embodiment, the solder balls preferably have a deformed spherical shape, wherein the aspect ratio is greater than one.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.08/948,751, filed on Oct. 10, 1997 and issued as U.S. Pat. No. 5,975,921on Nov. 2, 1999, herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to electrical connectors, and moreparticularly, to high density connectors intended for theinterconnection of daughter boards and back panels.

BACKGROUND OF THE INVENTION

Continued advances in the design of electronic devices for dataprocessing and communications systems have placed rigorous demands onthe design of electrical connectors. Specifically, electrical connectorshaving higher densities and pin counts are needed for design advanceswhich increase integration of solid state devices and which increase thespeed of data processing and communication. Designing connectors to havehigher densities and higher pin counts requires careful consideration ofthe problems which result from decreasing the distance between contacts.This is particularly true in applications involving daughter board/backpanel interconnections where the connector functions to establish anelectrical connection and functions to mechanically hold the daughterboard in position.

Density and pin count are often viewed interchangeably, but there areimportant differences. Density refers to the number of contacts providedper unit length. In contrast, the number of contact elements that canreasonably withstand the mating and unmating forces is referred to asthe pin count. As more functions become integrated on semiconductorchips or on flexible circuit substrates and more chips are provided onprinted circuit boards (PCBs), each PCB or flexible circuit must providemore inputs and outputs (I/Os). The demand for more I/Os directlytranslates to a demand for greater density without sacrificingelectrical or mechanical performance, particularly when such devices andintegration techniques are utilized in devices having back panels.

The importance of electrical performance of high density connectors wasrecognized in U.S. Pat. No. 4,824,383—Lemke, incorporated herein byreference. This patent proposed designs for plug and receptacleconnectors for multiple conductor cables or multiple trace substrates.In such designs electrical performance was assured by electricallyisolating individual contact elements or groups of contact elementsthrough the use of conductive walls to prevent or minimize crosstalk andsignal degradation. Although, the connectors disclosed in U.S. Pat. No.4,824,383 increased contact element density, industry driven densitydemands continued to grow. U.S. Pat. Nos. 5,057,028—Lemke et al. and5,169,324—Lenke et al. (now U.S. Pat. No. Re. 35.508), all incorporatedherein by reference, disclose two row plug and receptacle connectors forattachment to printed circuit boards (PCBs), which connectors againexhibited good electrical performance through the use of conductivewalls to provide isolation.

Electrical performance for high density connectors was also the focus ofU.S. Pat. Nos. 4,846,727, 5,046,960, 5,066,236, 5,104,341, 5,496,183,5,342,211 and 5,286,212. These patents disclose various forms ofstripline structures incorporated into a plug and receptacle system. Ina high density stripline structure, columns of contact elements arrangedin a side-by-side array with conductive plates disposed between eachcolumn. The connectors are designed so that the plug and receptacleground plates contact one another, thereby providing isolation betweencolumns. A further aspect of this system is the modular design of thereceptacle. Each column of receptacle contact elements is formed bymolding the contact elements into a frame of dielectric material. One ofthe problems with these types of connectors is that the use ofconductive walls for electrical isolation requires space. In certainapplications the space or volume necessary for such isolation isimpractical.

In those applications where space is critical, proposals for achievingdesired electrical performance have included the use of high densityconnectors in which one pin, selected for signal transmission, ispositioned between pins connected to ground. Such patterns are known asinterstitial arrangements. Such contact element patterns are suggestedin U.S. Pat. Nos. 5,174,770, 5,197,893 and 5,525,067. It will beappreciated that while such isolation schemes can be implemented in morecompact connectors, such schemes require greater numbers of pins thanwere available in the previously described connectors using conductivewalls.

In back panel applications, increasing the number of pins has a directimpact on mechanical integrity. As the number of pins increases, thenumber of bores or through holes in the back panel and daughter boardincreases. As the number of bores in a printed circuit board increaseswhile at the same time decreasing the distance between each bore, aswill be the case in high density applications, the mechanical integrityof the board decreases. As mechanical integrity decreases the abilityfor the back panel to mechanically hold the daughter board in positiondecreases.

It will be appreciated that in back panel applications, thedaughterboard is held in position, i.e., vertical and horizontalorientation, sometimes exclusively, by the connector used toelectrically interconnect the two. Daughterboard size, the number ofdaughterboards and the components mounted to the daughterboards combineto produce the stresses and moments acting on the back panel afterassembly. If the amount of back panel material is reduced in particularlocations due to larger numbers of closely spaced through bores, backpanel failure can occur, i.e., the back panel could deform or evenbreak.

One might conclude that the solution to back panel mechanical failurewould be to use surface mount techniques to establish electricalconnection to the back panel. Since surface mount techniques do notrequire the use of through holes, such techniques would afford theability to connect high density connectors to the back panel withoutimpacting mechanical integrity. Unfortunately, such solutions would beunsuccessful.

Surface mount techniques typically involve temporarily fixing acomponent to a printed circuit board using a paste. After pasting, theboard and temporarily fixed components are heated in order to reflowsolder material previously coated onto the leads of the surface mountcomponents. In back panel applications, numerous connectors are attachedto the back panel board, which is typically a relatively large circuitboard. In order to assure adequate reflow, thereby establishing goodelectrical connection, for numerous components spread over a relativelylarge board, the back panel board would have to be subjected tosignificant heat. Unfortunately, heat which is too high or too long induration can actually interfere with establishing good surface mountterminations. Consequently, surface mount techniques do not form theanswer to the need for higher density connectors for back panelapplications.

Consequently, a need still exists for a connector system which maximizesthe number of contact elements available for ground/signal assignmentand which does not jeopardize either the electrical or mechanicalintegrity of back panel applications.

One other consideration which must be taken into account when designinghigh density connectors, particularly for back panel applications is thedesign of the structure for attaching the receptacle portion of theconnector. One important factor in receptacle attachment is alignment.When a single receptacle contact element is misaligned, insertion forceincreases a negligible amount. However, when misalignment occurs in ahigh density contact receptacle, insertion force could increase tounacceptable levels. In other words, if misalignment occurs during themounting of a receptacle to a circuit board, it may become impracticalfor the board to be mounted to a plug or vice versa.

Consequently, a need still exists for a high density connector systemwhich provides sufficient alignment after mounting such that insertionforce remains within acceptable limits.

SUMMARY OF THE INVENTION

The above described problems are resolved and other advantages areachieved in novel high density electrical connectors. In one embodiment,the connector includes a base member having a plurality of bores. Afirst plurality of contact elements is positioned in certain of thebores. A second plurality of contact elements is positioned in others ofthe bores. The tail portion of each contact element extends a distancebeyond the base member. The insertion of the tail portion of the secondplurality of contact elements into circuit board through bores issufficient to hold the tail portions of the first plurality of contactelements against the circuit board.

It is preferred for the tail portions of the first plurality of contactsto be capable of axial movement when a compression force is applied. Inthis later embodiment, it is especially preferred for the tail portionsof the second plurality of contacts to include a serpentine structure.

In another embodiment, the connector includes a frame and a layer ofcontact elements, attached to the frame. Each of the contact elementsincludes a receiving portion and a tail portion. The ends of the tailportions are positioned proximate the bottom surface of the frame. Aplurality of fusible elements, for example, solder balls, are locatedproximate the ends of the tail portions. In such an embodiment, thesolder balls extend within a desired distance from the base. This resultis achieved by using solder balls having a deformed spherical shape. Itis especially preferred for the deformed spherical shape to have aflattened bottom surface.

In a still further embodiment, projections are attached to the bottom ofthe frame for keying and spacing said frame in relation to a printedcircuit board. In this embodiment, it is again preferred for the solderballs to have a deformed spherical shape, wherein the deformed sphericalshape is flattened, i.e., the aspect ratio of the solder ball includesgreater length than height.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood and its numerous objectsand advantages will become apparent by reference to the followingdetailed description of the invention when taken in conjunction with thefollowing drawings, in which:

FIG. 1 is a partial sectional view of a header constructed in accordancewith the resent invention;

FIG. 2 is a top view of the complete header depicted in FIG. 1;

FIG. 3 is a top view of the printed circuit board on which the header ofFIG. 1 is be mounted;

FIG. 4 is a diagrammatic side view of a receptacle constructed inaccordance with the present invention;

FIG. 5 is an enlarged diagrammatic view of the receptacle depicted inFIG. 4;

FIG. 6 is a still further enlarged view of an end of one of the contactelements having a solder ball mounted thereto;

FIG. 7 is a view of the contact element depicted in FIG. 6 after thesolder ball has been deformed in a manner in accordance with theinvention; and

FIG. 8 is a view of the contact element depicted in FIG. 7 and a printedcircuit board after the solder ball has reflowed establishing anelectrical connection between the contact element and the printedcircuit board.

DETAILED DESCRIPTION OF THE INVENTION

As was discussed above, one need which still exists in the industry is aconnector having greater density. To this end, a new connector 10 hasbeen developed and is generally depicted in FIG. 1. Although depicted asa plug, it will be appreciated that the invention is applicable toeither a plug or receptacle. Connector 10 is seen to include side walls12 and 14 and base wall 16. A number of blades 18 and 20 are disposed inbottom wall 16. It is noted that blades 18 include a deformable tailportion, preferably in the form of a press fit section which extends adistance below the bottom surface of bottom wall 16. By contrast, blades20 include a much shorter, compressible tail portion which extends onlya short distance from the bottom surface of bottom wall 16. It is notedthat the serpentine or S shape of the tail portion of blade 20 permitsthe tail portion to be compressed upon the exertion of force on thetail. FIG. 2 is a top view of plug 10.

Connectors constructed in accordance with the invention have theadvantage of requiring only half the pins having through holes while theother half utilizes contact pads for establishing electrical connection.In back panel applications, such a construction preserves the mechanicalintegrity of the back panel while providing a significantly higher pindensity. FIG. 3 depicts the portion of printed circuit board 22 ontowhich plug 10 is to be mounted. Circuit board 22 includes a pattern ofbores 24 and contact pads 26. It is noted that the diameter of thecontact pad is smaller than the diameter of the bore and that the boresand contact pads are arranged in an alternating pattern.

When plug 10 is mounted to circuit board 22, the tail portions of blades18 are inserted into bores 24. The force of insertion causes thecompressible end portions of blade 20 to establish electrical contactwith pads 26. It is preferred for the tail portions of blades 18 to beeither deformable or of a shape to cause a friction force between thetail portion and circuit board 22 sufficient to hold plug 10 in placeand maintain electrical contact between the tail portions of blades 20and contact pads 26.

Referring now to FIG. 4, connector 30, constructed in accordance withthe present invention will be described. Although depicted as areceptacle, it will be appreciated that the invention is applicable toeither a plug or receptacle. Connector 30 is shown diagrammatically toinclude a number of contact elements 32. It is noted that the contactelements are oriented in generally the same plane and are preferablyprovided as layer modules. Assembly of receptacle 30, thereby requiresthe stacking of a number of layers of contact elements in a side by siderelationship. As shown in FIG. 5, each layer of contact elementsincludes a positioning frame 34 formed from upstanding portion 36 andbase portion 38. It may be desirable during manufacture, to integrallymold portions 36 and 38 to a series of contact elements 32, therebyforming a contact element module.

One traditional method of mounting receptacle 30 to printed circuitboard 40 would have been through the use of extended tails 42 which passthrough appropriately sized bores in circuit board 40 for attachment bysoldering or the like. However, as was pointed out in relation to theplug being mounted to circuit board 22 in FIG. 3, bore size can have alimiting effect on contact element density. To this end, the receptacleof the present invention includes a novel structure for establishingelectrical contact between module 30 and circuit board 40.

The present invention utilizes fusible elements, for example, solderballs for mounting module 30 to board 40. Because module 30 is a highdensity module, the use of solder balls will be sufficient to establishboth electrical contact as well as providing sufficient mechanical forcefor maintaining the attachment of module 30. To this end, a pattern ofcontact pads (not shown) are disposed on the surface of circuit board40.

A keying peg 44 is provided on base portion 38 for aligning the tailends of contact elements 32 above individual contact pads. Shoulder 46and leg 48 serve to space the bottom of base portion 38 from the top ofcircuit board 40. It may be desirable to precisely fix this distance. Aswill be explained in greater detail in relation to FIGS. 6-8, contactelements 32 are electrically connected to contact pads (not shown) onthe surface of circuit board 40 through the use of solder balls.

Referring now to FIG. 6, the end of one of the contact elements 32 isdisclosed. A fusible element, for example, solder ball 50 is shownattached to end 52. Attachment of solder ball 50 can be by any suitablemeans, for example by reflowing techniques. It is noted that the bottomsurface of base 38 extends a short distance beyond the end surface ofend 52. In other words, the end surface of end 52 is recessed withinbase portion 38. After attachment of solder ball 50 to end 52 the solderball extends beyond the bottom surface of base portion 38.

Although the use of solder balls permits high density connection withoutthrough bores, one problem still remains. Because the solder ballsextend beyond the bottom surface of base portion 38, connector 30 may besuspended a short distance above the circuit board when the connector isassembled onto a circuit board. In such a situation, when solder balls50 are reflowed in order to establish electrical connection with thecontact pads (not shown), movement, i.e., re-alignment, of module 30will occur. Such re-alignment can cause insertion force to rise tounacceptable levels. This problem has been largely overcome by thepresent invention.

In the present invention, the fusible elements are deformed to yield anaspect ratio in which length (the dimension parallel to the circuitboard to which the connector is to be mounted) is greater than theheight (the dimension parallel to a line from the point of attachment tothe circuit board to the frame). In such a case, the aspect ratio of thefusible element is greater than one. In other words, the fusible elementor solder ball is wider than it is high.

Consider briefly, techniques for positioning deformed fusible elements,such as solder balls, on the ends of contact elements 32. Two generaltechniques are envisioned. In the first technique, the fusible elements,such as solder balls, are forcibly pressed onto the ends of elements 32and thereafter deformed. The deformation process can include eitherfixing the frame and pressing or striking a platen-like device (notshown) against the bottom surface of each solder ball or by pressingeach solder ball against an anvil-like device. In either case, thesolder ball is preferably deformed to have a flattened shape.

In the second technique for attaching fusible elements, such as solderballs, onto the ends of contact elements 32, the fusible elements areplaced near the ends or terminal stubs of the contact elements andsubjected to heat in order to cause reflow to occur. Reflow will causethe fusible elements to become attached to the terminal stubs.Thereafter, the fusible elements are deformed. Again, the deformationprocess can include either fixing the frame and pressing or striking aplaten-like device against the bottom surface of each fusible element orby pressing each solder ball against an anvil-like device. In eithercase, the fusible elements are again preferably deformed to have aflattened shape.

Consider the case where solder balls are used as the fusible element.After manufacturing it is probable that the ends of the solder balls mayextend beyond the spacing distance established by shoulder 46 and leg48. In other words when the connector is placed onto the circuit boardit may initially be supported by certain of the solder balls rather thanshoulder 46 and leg 48. When the solder melts, as during during reflow,the connector will physically move towards the circuit board, therebyrealigning the connector. When flattened or deformed (aspect ratiogreater than 1) solder balls are used, the connector moves a shorterdistance. Accordingly, the opportunity for misalignment is significantlyless, because, prior to reflow, the connector is in a position closer tothe desired position in three dimensions (x, y and z). Having theconnector positioned as close to the ultimate z position as possible,prior to reflow, is most critical.

In particular, referring to FIG. 7, it will be seen that solder ball 50has been deformed, preferably by exerting a compression force on thesolder ball. The exertion of such a compression force deforms the solderball out of a spherical shape to preferably having a flattened bottomshape, i.e., an aspect ratio greater than one. When solder ball 50 isreflowed, it returns to a spherical shape eliminating the collapsed ordeformed shape and changing the elevation of the connector. An exampleof such a reflowed solder ball is shown in FIG. 8. As can be seen fromFIG. 8, solder ball 50, after reflow, has extended a distance such thatelectrical contact is now made between circuit board 40 and end 52 ofcontact element 32.

It has been discovered that when solder balls are reflowed, themechanical forces generated during such operations cause re-alignment ofthe connector. Such re-alignment can cause insertion forces betweenmating connectors to rise to unacceptable levels. However, by firstshaping the solder balls, as shown in FIG. 7, the degree of re-alignmentwhich occurs is significantly reduced. Insertion forces following reflowof deformed solder balls do not rise to unacceptable levels.

Thus it will be seen that by utilizing deformed solder balls forestablishing electrical contact with circuit board 40, electricalconnection can be established in a much smaller surface area thanheretofore realizable, thereby significantly increasing the potentialfor contact element density.

While the invention has been described and illustrated with reference tospecific embodiments, those skilled in the art will recognize thatmodification and variations may be made without departing from theprinciples of the invention as described hereinabove and set forth inthe following claims.

What is claimed is:
 1. An electrical connector adapted to mount on asubstrate, comprising: a body; a plurality of contact elements attachedto said body, each having a mounting portion; and a plurality of formedbodies, each having a first shape before being secured to said mountingportion of a respective one of said contact elements and having a secondshape, now including a deformed region that did not exist in said firstshade, after being secured to said mounting portion of said contactelement, said second shape being different than said first shape;wherein said deformed regions provide a generally planar surface forsubsequent placement onto the substrate.
 2. The electrical connector asrecited in claim 1, wherein said formed bodies comprise masses ofsolder.
 3. The electrical connector as recited in claim 2, wherein saidmasses of solder are solder balls.
 4. The electrical connector asrecited in claim 3, wherein said deformed regions comprise flattenedbottoms on said solder balls.
 5. The electrical connector as recited inclaim 1, wherein said body has a mounting face positionable adjacent thesubstrate, said formed bodies extending past said mounting face.
 6. Theelectrical connector as recited in claim 5, wherein said contactelements are recessed within said mounting face.
 7. The electricalconnector as recited in claim 1, wherein said formed bodies surround adistal end of said contact elements.
 8. An electrical connector adaptedfor mounting to a circuit substrate, wherein prior to mounting on thecircuit substrate, the connector comprises: a body having a mountingportion for facing the substrate; a plurality of contact elementsattached to said body; and a plurality of formed bodies having a firstshape before being secured to said contacts and a second shape,different than said first shape, after being secured to said contactswhich now includes a generally planar area facing away from saidmounting portion that did not exist in said first shape so that saidbodies, except for said generally planar area, are generallycurvilinear.
 9. The electrical connector as recited in claim 8, whereinsaid formed bodies are masses of solder.
 10. The electrical connector asrecited in claim 9, wherein said masses of solder are solder balls. 11.An electrical connector adapted for mounting to a circuit substrate,wherein prior to mounting on the circuit substrate, the connectorcomprises: a body having a mounting portion for facing the substrate; aplurality of contact elements attached to said body and recessed withinsaid mounting portion; and a plurality of formed bodies having a firstshape before being secured to said contacts and a second shape,different than said first shape, after being secured to said contacts sothat said bodies, except for a generally planar area facing away fromsaid mounting portion for engaging the circuit substrate, are generallycurvilinear.
 12. The electrical connector as recited in claim 11,wherein said formed bodies surround a distal end of said contactelements.
 13. A method of making an electrical connector mountable on asubstrate, comprising the steps of: providing a body with a plurality ofcontact elements secured thereto, each contact element having a mountingportion; attaching a formed body having a first shape to each of saidmounting portions; and deforming said formed bodies to create a secondshape, different than said first shape, and including a deformed regionthat did not exist in said first shape and which provides a generallyplanar surface adapted for subsequent placement onto the substrate. 14.The method of making an electrical connector as recited in claim 13,wherein the deforming step occurs subsequent to the attaching step. 15.The method of making an electrical connector as recited in claim 13,wherein the attaching step comprises reflowing said formed body.
 16. Themethod of making an electrical connector as recited in claim 15, whereinsaid formed body is a mass of solder.
 17. The method of making anelectrical connector as recited in claim 16, wherein said mass of solderis a solder ball.
 18. The method of making an electrical connector asrecited in claim 12, wherein the attaching step comprises pressing saidformed bodies and said contacts against each other.
 19. The method ofmaking an electrical connector as recited in claim 13, wherein thedeforming step comprises pressing said formed bodies and a surfaceagainst each other.
 20. The method of making an electrical connector asrecited in claim 13, further comprising the steps of: providing acircuit substrate; and attaching the electrical connector to saidcircuit substrate subsequent to the deforming step.
 21. An electricalconnector mountable to a substrate, comprising: an insulative housinghaving an opening therein; a contact in said opening; and a formed bodysecured to said contact and including: a first portion within saidopening; a second portion outside of said opening; and a deformed regionon said second portion; wherein said deformed region provides agenerally planar surface for subsequent placement of the connector tothe substrate.
 22. The electrical connector as recited in claim 21,wherein said formed body secures to a tail end of said contact, saidtail end residing within said opening.